Implement initializer() for FileDesc

in order to avoid constantly zeroing memory when it's not needed.

src/libstd/sys/unix/fd.rs

@@ -11,7 +11,7 @@
 #![unstable(reason = "not public", issue = "0", feature = "fd")]
 
 use cmp;
-use io::{self, Read};
+use io::{self, Read, Initializer};
 use libc::{self, c_int, c_void, ssize_t};
 use mem;
 use sync::atomic::{AtomicBool, Ordering};
@@ -270,6 +270,11 @@ impl<'a> Read for &'a FileDesc {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         (**self).read(buf)
     }
+
+    #[inline]
+    unsafe fn initializer(&self) -> Initializer {
+        Initializer::nop()
+    }
 }
 
 impl AsInner<c_int> for FileDesc {